A semiconductor integrated circuit device includes a write-read clock control signal generating unit that activates a read clock control signal and a write clock control signal in response to one of a write operational mode and a read operational mode after maintaining the read clock control signal and the write clock control signal at a deactivation state in response to one of an idle mode and a refresh operational mode, and a clock buffer that generates a read clock signal and a write clock signal in response to a clock signal, the read clock control signal, and the write clock control signal.